The present invention relates to a method for the accelerated bioremediation of contaminated material and to a method of using an apparatus therefor, and more particularly to the accelerated bioremediation of contaminated material treated with chemical and/or biological amendments.
Bioremediation in general involves the degradation of contaminated material, typically by the action of contaminate degrading aerobic bacteria. When practiced on a small scale, it is relatively easy to maintain the aerobic conditions required by the bacteria; it is much more difficult to do on a larger scale. Failure to maintain aerobic conditions throughout the contaminate material results in anaerobic decay of the material, which is much less efficient and much more time consuming than aerobic decomposition. This provides strong incentive to maintain aerobic reaction conditions at all times.
The biological degradation of hydrocarbons can be conducted employing specialized bacteria that utilizes hydrocarbons as their sole metabolic carbon source or as a co-metabolite. The bacteria produce enzymes which catalytically crack the covalent carbon-hydrogen bonds of hydrocarbons so that the smaller resulting molecules may pass through the cell wall of the bacterial organism for nutrient. In some instances, the bacteria may produce enzymes which crack a carbon bond on an alternate carbon source such as a carbohydrate. This same enzyme may also crack the hydrocarbon. This is called co-metabolism.
In addition to a carbon source, most living organisms require a balance of other nutrients such as nitrogen, phosphorus, various minerals in micro quantities, etc. to efficiently metabolize and reproduce. Any specific nutrient that is deficient in a given biological system will limit the efficiency of that system. This is akin to the "basic 4 food groups" idea of human nutrition which includes protein as a nitrogen source, carbohydrate as a carbon source, dairy as a fat or fatty acid source plus phosphorus and a large number of vegetables as a vitamin and mineral source. Although bacterial requirements may be different from humans, a balanced nutritional system is required for optimal bacterial activity.
There are thousands of identified sites in the United States containing hazardous wastes. For most of these sites, the recognized methods for closure are:
1. Cap and store-in-place PA1 2. Removal to an approved hazardous waste landfill. PA1 3. Solidify in place with fixation chemicals PA1 1. Treatment of industrial wastewater through biological oxidation under an NPDES permit. PA1 2. Treatment of on site chemicals through controlled release to an NPDES-permitted system (many states allow this through a temporary permit amendment). PA1 3. Treatment of leachates collected under hazardous waste sites. In some cases a cone of depression can be created to leach organics out at a rapid rate. PA1 4. Land farm of sludges and solid-containing organics. PA1 This includes additional soil borings, groundwater monitoring and chemical analyses to determine the site contamination characteristics. PA1 This is usually researched into the treatability of chemicals found in the site. PA1 The soil must be analyzed for pH, macronutrients (N,P,K), micronutrients (usually trace metals), permeability, moisture content and other conditions which will determine its suitability for land farming. PA1 A chemical protocol is established to allow monitoring of the land farm. This is a two-tier protocol consisting of: PA1 Using the site characteristics, the land farm is simulated and efficiency of the treatment is proven. Samples of decontaminated soil and sludge may be presented for reference analyses. PA1 The consultant and land farm specialists designate the portion of the closure site to be used for the land farm and design excavation schedules, aeration and mixing techniques, irrigation method, run-off collection, and decontaminated soil removal and disposal method. PA1 Beginning with a surface treatment of the site to be used, the land farm is begun. After control testing shows a desired level of treatment, toxicology tests are made. The soil may then be decontaminated and removed, if desired. Land farming is then usually continued in 12" lifts. PA1 Decontaminated sludges and soils are removed to a nonhazardous waste landfill or landfilled on-site.
In addition to the methods generally known, many industrial plants have used biological solutions to effect closures. Quite a few biological cleanups took place prior to the effect of the RCRA and TSCA legislation. Now under the formal guidelines of current hazardous waste regulation, use of biological treatment can offer an economical alternative to the methods listed above.
Biological treatment of hazardous waste chemicals can take the following forms:
Land farming is of principle interest due to the large numbers of area sites with contaminated sludges and soils.
A key issue in a hazardous waste site closure is permitting land farms. Often obtaining such a permit is not feasible under existing regulations. In most cases, those regulations were intended to address new land farms. Land farming is a biochemical process which operates at low biological reaction rates. The variables controlling total cleanup time in a land farm are initial substrate concentrations, desired treatment levels, area available for land farm and turnaround time to dispose of decontaminated sludge or soil. Many hazardous waste sites could be successfully land farmed in 6-12 months, after pilot work is complete.
The actual protocol for land farming a particular site should be established for each site by a combination of pilot testing and practice. A typical protocol for land farming a hazardous waste site would be as follows:
1. CHARACTERIZATION OF THE SITE PA0 2. CHARACTERIZATION OF THE ORGANICS AS TO BIODEGRADABILITY PA0 3. CHARACTERIZATION OF THE SOIL PA0 4. CRITERIA FOR SUCCESSFUL LAND TREATMENT PA0 5. BENCH SCALE LAND FARM TREATMENT PA0 6. DESIGN OF LAND FARM TREATMENT PA0 7. IMPLEMENTATION OF LAND FARM TREATMENT PA0 8. CLOSURE
A. Control analyses to allow quick determination of treatment progress during the land farming. PA2 B. Objective toxicity testing to be used when control analyses indicate that the treatment is complete. This includes all testing for leachate priority pollutants.
The above steps are difficult and timely in their performance and extremely costly to the end user.
There are known machines for physically mixing materials in the field such as compost to maintain aerobic conditions. An example is U.S. Pat. No. 4,360,065 to Jenison et al. The Jenison cultivator comprises a horizontal rotating drum having a plurality of cultivator blades in two helical rows. As the drum is rotated, the blades travel edgewise through a pile of composting material to move the material sideways and pile it in a generally triangular pile. The '065 patent further describes other composting machines such as the Scarab, sold by Scarab Manufacturing and Leasing, Inc. of White Deer, Tex. U.S. Pat. No. 3,369,797 to Cobey describes a compost turner and windrow forming machine having a transversely mounted rotating drum for the turning of compost piles and the redepositing of the turned up material in a windrow. Yet another composting apparatus is described in U.S. Pat. No. 4,019,723 to Urbanczyk. The '723 patent describes a mobile composter for manure which moves a rotating drum over masses of inoculated manure to flail it, mix it, cool it and aerate it, while moistening the particles as the same time. After being conditioned and moisturized, the material is formed into a pile by a rear outlet opening. As with the Cobey composter, the flails mounted on the drum of the Urbanczyk machine travel edgewise through the composting material for flailing and mixing. U.S. Pat. No. 4,478,520 also to Cobey describes a compost turning machine which straddles a compost windrow while carrying a rotating drum for turning the composting material. The '520 composter additionally has an adjuster auger system outboard of the rotating drum to collect additional material and deposit it in the path of the rotating drum. This is the Cobey machine referred to earlier.
A need therefore exists for a method of bioremediation which will overcome the problems associated with the above described prior art methods by substantially eliminating the contaminants from contaminated material in an effective, efficient and accelerated manner.